To expand on what TheKindleWorm posted you can download MobleRead's
MobiPocket Download Guide. It's a "book" you put on your Kindle (in the documents folder) that has descriptions and links to all the free mobi versions of books in the MR Patricia Clark library. With your Kindle's wireless turned on, you just click on a title and it will download to your Kindle. Each book has been formatted and error corrected by MobileRead members, so you will get a high quality ebook (for FREE).
A similar guide for Kindles can also be found at
Feedbooks.